Neurological injury, such as hemiparesis from stroke, results in significant muscle weakness or impairment in motor control. Patients experiencing such injury often have substantial limitations in movement. Physical therapy, involving rehabilitation, helps to improve the walking function. Such rehabilitation requires a patient to practice repetitive motion, specifically using the muscles affected by neurological injury. Robotic rehabilitation can deliver controlled repetitive training at a reasonable cost and has advantages over conventional manual rehabilitation, including a reduction in the burden on clinical staff and the ability to assess quantitatively the level of motor recovery by using sensors to measure interaction forces and torques in order.
Currently, available lower extremity orthotic devices can be classified as either passive, where a human subject applies forces to move the leg, or active, where actuators on the device apply forces on the human leg. One exemplary passive device is a gravity balancing leg orthosis, described in U.S. patent application Ser. No. 11/113,729 (hereinafter “the '729 application”), filed Apr. 25, 2005, and assigned to the assignee of the present invention, incorporated herein by reference. This orthosis can alter the level of gravity load acting at a joint by suitable choice of spring parameters on the device. This device was tested on healthy and stroke subjects to characterize its effect on gait.
Passive devices cannot supply energy to the leg, however, and are therefore limited in their ability compared to active devices. Exemplary active devices include T-WREX, an upper extremity passive gravity balancing device; the Lokomat® system, which is an actively powered exoskeleton designed for patients with spinal cord injury for use while walking on a treadmill; the Mechanized Gait Trainer (MGT), a single degree-of-freedom powered machine that drives the leg to move in a prescribed gait pattern consisting of a foot plate connected to a crank and rocker system that simulates the phases of gait, supports the subjects according to their ability, and controls the center of mass in the vertical and horizontal directions; the AutoAmbulator, a rehabilitation machine for the leg to assist individuals with stroke and spinal cord injuries and designed to replicate the pattern of normal gait; HAL, a powered suit for elderly and persons with gait deficiencies that takes EMG signals as input and produces appropriate torque to perform the task; BLEEX (Berkeley Lower Extremity Exoskeleton), intended to function as a human strength augmenter; and PAM (Pelvic Assist Manipulator), an active device for assisting the human pelvis motion. There are also a variety of active devices that target a specific disability or weakness in a particular joint of the leg.
A limiting feature of existing active devices, however, is that they move a subject through a predestined movement pattern rather than allowing the subject to move under his or her own control. The failure to allow patients to self-experience and to practice appropriate movement patterns may prevent changes in the nervous system that are favorable for relearning, thereby resulting in “learned helplessness,” which is sub-optimal. Fixed repetitive training may cause habituation of the sensory inputs and may result in the patient not responding well to variations in these patterns. Hence, the interaction force between the human subject and the device plays a very important role in training. For effective training, the involvement and participation of a patient in voluntarily movement of the affected limbs is highly desirable. Therefore, there is a need in the art for devices that assist the patient as needed, instead of providing fixed assistance.